1. Field of the Invention
The invention relates to a flame retardant, low smoke emission, halogen free 600 V energy cable with polyolefin insulation and polyamide jacket, having improved performance properties as compared to common thermoplastic high heat-resistant nylon-coated (THHN) and thermoplastic high heat water-resistant-low smoke (THHW-LS) type cables, wherein the combined advantages result in a flame retardant having low smoke emission, halogen free cable, and resistant to aggressive environments, oils, greases and gasoline according to Mexican standard ANCE NMX-J-010-ANCE-2005.
2. Description of the Prior Art
Currently manufactured THHN-type cables are made of cable or wire copper or aluminum conductors, with polyvinyl chloride (PVC) based thermoplastic insulation and polyamide (nylon) jacket, said cables are appropriate for electrical installations of up to 600 V, resistant to abrasion, oils, greases, gasoline and chemical agents. Moreover, THHW-LS are cables with a copper conductor and polyvinyl chloride based insulation with flame retardant characteristics, low emission of obscure smoke and acidic gas fulfilling Mexican Standard ANCE NMX-J-010-ANCE-2005.
A thermoplastic high heat water-resistant-low smoke zero halogen (THHN-LSZH)-type cable was developed which combines the performance characteristics of both THHN and THHW-LS cable types with the combined advantages of both cable types: resistance to aggressive environments, oils, greases, and gasoline together with low smoke emission and resistance to flame propagation according to Mexican Standard ANCE NMX-J-010-ANCE-2005. Moreover, these new cables do not contain halogen that produces acidic gases when the cable is burnt.
Some cables are manufactured with insulation and other layers, thus forming multi-layer cables that act globally as composed material with unique properties resulting from the combination of the properties of the individual materials, as in this case the two layers: insulation conferring high performance electrical insulation properties and the nylon jacket conferring mechanical and chemical resistance properties.
The combination of both layers offers moreover flame retardancy, low smoke emission and halogen free composition. A disadvantage of the insulated cables based on PVC is that during their combustion, they emit acidic gases that are a health risk and a risk for the environment because they also corrode metals, said characteristic being especially important in areas where there could be equipment and instrument with components susceptible to corrosion.
There are some patents related to the invention, such as patent EP 0631 538 BI “IMPROVED FLEXIBLE FIRE RETARDANT MULTI-LAYER STRUCTURES COMPRISING POLYOLEFIN AND POLYAMIDE LAYERS AND PROCESS FOR MAKING SAME”.
The instant invention presents advantages compared to the above mentioned patent, in that this cable generates low smoke emission measured as: specific maximum density, obscuration value due to fume during the first 4 minutes (VOF4) and vertical tray flame test.
It is an object of the instant invention to supply a low smoke emission, halogen-free cable for electrical installations of up to 600 V THHN-LSZH type, Afumel trademark pending, the construction of said cable is as described hereinafter:                Copper or aluminum conductor, wire or cable;        Thermoset compound insulation based on flame retardant polyolefin cross linked through moisture;        Flame retardant polyamide (Nylon-6) jacket.        
Because it has a nylon jacket, this cable shows reduced insulating thicknesses as in the case of THHN type cables but with THHW-LS cable properties with regard to low smoke emission (Maximum specific density Dm and obscuration value due to fume during the first 4 minutes (VOF4), said characteristic cannot be fulfilled with a conventional THHN cable with a natural nylon jacket because the nylon, upon burning, generates a considerable amount of obscure smokes; this is not the case of the flame retardant nylon used in the THHN-LSZH cable that in this case also fulfills the vertical tray flame test as a complete cable.
The THHN-LSZH Afumel type 600 V energy cable 10, FIG. 1 and FIG. 2, object of the instant invention comprises:
a) an electric conductor core 11 made of copper or aluminum based on a plurality of wires 14. The conductors used can be individual wires or soft copper cables with electrical resistivity no greater than 17,241 nOhm.m (0.15328 Ohm.g/m2) corresponding to an IACS 100% conductivity or aluminum with electrical resistivity not greater than 28,264 nOhm.m (0.07639 Ohm.g/m2) equivalent to an IACS 61% conductivity, the cabled conductors are made of wire layers with combined alternate laying in the gauge range from 14 to 2 AWG and compressed laying in the gauge range from 1 AWG to 1000 MCM.b) Then, the wire core comprising a layer 12 of anti-flame insulation based on a silane cross-linked polyethylene system (polyamide) comprising a mixture of: 90-99% parts of high density 100% natural resin and from 1 to 10% catalyzing additive (from 0.5 to 5.0% of tin dibutyl dilaurate, and from 0.5 to 7.5% of zinc stearate) providing thermal stability upon cross linking the (stripped) polyethylene chains transforming it in a thermoset material and flame retardant additive based on polyethylene resin mixed with phosphorus and nitrogen. The ratio of the components is constant independently of the thickness of the insulating layer indicated in Table No. 1; and c) A flame retardant nylon-6 jacket 13 with low smoke emission.
The jacket is based on non halogenated phosphorated flame retardant nylon-6 (6-aminohexanoic acid). The composition of this jacket is constant, independently of the thickness indicated in Table No. 1. The plastic cover of the cable is composed of two layers, the first layer being the insulating layer that is in contact with the conductor and based on an extruded silane cross-linked polyethylene system, the cross-linking or curing of the polyethylene is conducted through exposition to environmental moisture because of the components contained in its formulation. The preparation of silane cross-linked polyethylene is well known in the art. See for example, U.S. Pat. No. 3,646,155; U.S. Pat. No. 3,225,018 and GB1286460, the disclosures of which are incorporated herein by reference. The second layer, or jacket, is based on flame retardant nylon-6 and applied by tandem extrusion; i.e., in one single manufacturing line an extruder is used for the first insulating layer and thereafter on the same line, the second extruder is located that applies the nylon jacket. The thicknesses of the two layers, insulating layer and nylon jacket, are indicated in Table No. 1.
Hereinafter Table No. 1 describes the dimensional size of the THHN Afumel cable.
TABLE NO. 1DiameterNYLONof theINSULATIONJACKETstrippedTHICKNESSTHICKNESSTHHN-LSZH AfumelconductorMinimumMinimumtype cable(mm)mmmm14 AWG 90° C. 600 V1.800.380.1112 AWG 90° C. 600 V2.2910 AWG 90° C. 600 V2.870.518 AWG 90° C. 600 V3.630.760.146 AWG 90° C. 600 V4.534 AWG 90° C. 600 V5.701.020.162 AWG 90° C. 600 V7.201 AWG 90° C. 600 V8.181.270.191/0 AWG 90° C. 600 V9.192/0 AWG 90° C. 600 V10.313/0 AWG 90° C. 600 V11.584/0 AWG 90° C. 600 V13.00250 Kcm 90° C. 600 V14.181.520.21300 Kcm 90° C. 600 V15.53350 Kcm 90° C. 600 V16.77400 kCM 90° C. 600 V17.94500 kCM 90° C. 600 V20.05600 kCM 90° C. 600 V21.991.780.24700 kCM 90° C. 600 V23.76750 kCM 90° C. 600 V24.581000 kCM 90° C. 600 V28.39
Hereinafter, the manufacturing process of THHN-LS-ZH cable is described:
1) The electric conductor of the cable is conventionally manufactured through the standard drawing and joining processes of copper or aluminum wires.
2) Application of insulating and nylon jacket through tandem extrusion process, i.e., the two insulating layers are applied in one single step.
3) The insulating material is based on polyolefin that is chemically cross-linked through moisture. This cross-linking of the polymer chain is obtained through the addition of silanes; the final result is the obtaining of a thermoset compound, the mixture is prepared according to the following ratios:
Polyethylene-based resin: 90% to 99%
Catalyst: 1% to 10%
In the example mentioned hereinafter, the differences between THHN-LSZH and THHW-LS cables are shown.